A PDP (for example, a three electrode surface discharge type PDP) has a structure in which a front panel that forms a surface side as viewed by a person who takes a look at an image, and a rear panel are oppositely disposed to each other, the peripheries of the front panel and the rear panel being sealed by a sealing material. Between the front panel and the rear panel, there is formed a discharge space filled with a discharge gas (neon, xenon or the like). The front panel is provided with a glass substrate, a display electrode pair comprising a scan electrode and a sustain electrode formed on one surface of the glass substrate, and a dielectric layer and a protective layer that cover these electrodes. The rear panel is provided with a plurality of address electrodes formed on the glass substrate in the form of stripes in a direction that perpendicularly intersects to the display electrode pair, a base dielectric layer that covers the address electrodes, barrier ribs serving to partition the discharge space with respect to every address electrode, and phosphor layers (red, green and blue fluorescent layers) coated on the base dielectric layer and the sides of the barrier ribs.
The display electrode pair and the address electrode perpendicularly intersect to each other, and each intersection portion thereof serves as a discharge cell. These discharge cells are arranged in the form of a matrix, and three discharge cells having red, green and blue fluorescent layers, arranged in the direction of the display electrode pair, serve as picture elements for color display. In the PDP, a predetermined voltage is sequentially applied between the scan electrode and the address electrodes, and between the scan electrode and the sustain electrode to generate gas discharge. Then, the phosphor layers are excited by ultraviolet rays generated by the gas discharge, and thereby emitting visible lights, which leads to a realization of a full-color display.
Significant progress has recently been made in realization of higher definition of PDP to a high definition television in which the number of scanning lines is two or more times larger than an NTSC system of the prior art. At the same time, with the progress of a display with a larger screen, voltage and electric power required to display images necessarily increase, and thus it is required to decrease a resistance value of the display electrode.
In order to decrease the resistance value of the display electrode, the cross-sectional area of the electrode must be increased. However, when the electrode width is increased, an aperture area, through which visible lights of picture elements to be image-displayed is transmitted, becomes smaller, leading to a decrease in an image display brightness of the PDP. In contrast, when the thickness of the electrode increases, there arises a problem that the thickness of the dielectric layer provided on the electrode substantially becomes smaller, leading to a decrease in a dielectric strength voltage.
Therefore, a trial has been conducted of increasing an amount of thermal shrinkage of a metal bus electrode attributable to a heat history of the calcining step as the step after the development to densely form an electrode film, by increasing an amount of a so-called “undercut” of the bus electrode after the development, namely, by controlling the value of a difference between a projection width W2 of bus electrodes (12b, 13b) to 25 μm or more and a width W1 being in contact with the substrate of the bus electrodes (12b, 13b) as shown in FIG. 7. Whereby, the contact points between silver particles can be increased, thus making it possible to improve an electric conductivity of the bus electrode (see Literature 1 described below, for example).
For example, literature disclosing the conventional PDP producing method are as follows:
Literature 1: JP-A-2008-293867
Literature 2: JP-A-2008-282707
As a result of increasing the contact points between silver particles (silver powders) by densifying the electrode film, the electric conductivity between the particles can be increased. However, since silver particles are merely in point contact with each other even after calcining, a decrease in the resistance value is still small even in the case of the dense film. Furthermore, when the amount of the undercut increases, the amount of a warp (amount of “edge curl”) of the end of the bus electrode increases, the warp amount being generated by a difference in a thermal shrinkage between the white layer and the black layer. Namely, as shown in FIG. 8, a value of a difference between “film thickness H1 at the center in a width direction of bus electrodes (12b, 13b)” and “film thickness H2 at the end of bus electrodes (12b, 13b)” increases. As a result, a substantial film thickness of the dielectric layer around the edge curl decreases, and thereby a dielectric strength voltage decreases (see FIG. 9 regarding “edge curl”, and also see the above Literature 2 regarding a generation of “edge curl”). In particular, in a case in which the dielectric layer is formed from a sol-gel material, a level-difference is generated in a surface of the dielectric layer due to an increase in the amount of the edge curl and thus cracking is likely to generate in the dielectric layer, which causes a risk of a decrease in the dielectric strength voltage.
Under the above circumstances, the present invention has been created. Thus, an object of the present invention is to provide a PDP with a decreased resistance of the bus electrode, and another object thereof is to provide a PDP with a suppressed edge curl of the bus electrode.